The present invention relates generally to lithography and more particularly relates to a system and method for measuring films associated with lithography processes or other type semiconductor fabrication processes.
In the semiconductor industry there is a continuing trend toward higher device densities. To achieve these high densities there has been, and continues to be, efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such a high device packing density, smaller features sizes are required. This may include the width and spacing of interconnecting lines and the surface geometry such as the comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which, for example, a silicon wafer is coated uniformly with a radiation-sensitive film (e.g., a photoresist), and an exposing source (such as ultraviolet light, x-rays, or an electron beam) illuminates selected areas of the film surface through an intervening master template (e.g., a mask or reticle) to generate a particular pattern. The exposed pattern on the photoresist film is then developed with a solvent called a developer which makes the exposed pattern either soluble or insoluble depending on the type of photoresist (i e., positive or negative resist). The soluble portions of the resist are then removed, thus leaving a photoresist mask corresponding to the desired pattern on the silicon wafer for further processing.
As process designers continue to shrink the size of the features which make up various semiconductor components, various process parameters must be tightly controlled. For example, in order to provide small, repeatable feature sizes, the thickness of various films such as photoresist layers and anti-reflective coatings (ARCs) must be small and uniform about the surface of the wafer. Consequently, process designers regularly measure the thickness of such films.
Film thicknesses typically are determined using characterization equations provided by the tool manufacturers which use various film material constants such as absorption coefficients and optical constants such as the index of refraction. Using such equations, process developers can implement various tests and take various parametric measurements, insert the measured data into the equations, and calculate an approximate film thickness. Although such thickness determination techniques are modestly accurate, the characterization equations require that the various film material constants which characterize the film be known. For newly developed materials such as next generation photoresists and ARC materials, such advanced characterization data is not easily available, thus making the determination of such film thicknesses difficult.
The present invention relates to a system and method of measuring accurately a film thickness without the use of film material characterization data.
According to one aspect of the present invention, the system and method of measuring a film thickness includes identifying a location of a defect, for example, a crystalline defect, in an underlying material such as a semiconductor substrate. Using the defect location information, the depth or height of the defect is measured using, for example, a topography evaluation tool. After the film to be measured is formed over the underlying material, the defect, which is reproduced in the overlying film, is again measured to identify the depth or height associated therewith. Using the measured pre-film and post-film defect depth data, the film thickness is determined. The present invention avoids the need to have characterization data associated with the film to be measured and thereby facilitates process development using new and/or advanced film materials.
According to another aspect of the present invention, a method of determining a film thickness includes identifying a location of one or more defects such as pits or crystal-originated particle defects in a material such as a semiconductor wafer. Once the defect location(s) is identified, the location data is used to measure the depth or height of the defect(s). Subsequently, the film to be measured is formed over the material and, because the film generally is conformal, the defect(s) is reproduced therein. Again, using the defect location data, the depth or height of the defect(s) are measured. The defect depth/height data (both prior to film formation and after film formation) is then utilized to calculate the film thickness without the need of characterization data related to the film material. In addition, if multiple defects exist, the multiple data points may be utilized to determine an average film thickness along with other statistical data.
According to another aspect of the present invention, a system for determining a film thickness is disclosed. The system includes a defect inspection tool, a topography measurement tool and a processor. The defect inspection tool evaluates an underlying material such as a semiconductor substrate to identify a location associated with one or more defects and transmits the location data to the processor. The processor then uses the location data to control the positioning of the topography measurement tool in order to collect depth or height data. The topography measurement tool identifies the depth or height associated with the one or more defects and transmits the defect depth/height data to the processor. After the film to be measured is formed over the underlying material, the processor and topography measurement tool again interface to collect the defect depth/height data associated with the one or more defects which are reproduced in the overlying film. Using the defect depth/height data, the processor determines the film thickness without the need for film characterization data, thus substantially facilitating process development associated with new materials.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.